Dynamo-electric machine



A. G. WILLIAMSON DYNAMO-ELECTRIC MACHINE March s, 1938 Filed March 4, 1936 Inventor Alexander GWiHi'amson Patented Mar. s, 1938 2,110,719

UNITED STATES PATENT FFWE DYNAMO-ELECTRIG MACHINE Alexander Greenwood Williamson, Manchester, England, assignor to General Electric Company, a corporation of New York Application March 4, 1936, Serial No. 67,152 In Great Britain March 16, 1935 6 Claims. (01. 17l223) My invention relates to dynamo-electric madiametrically opposite pole pieces and 3 and are chines and particularly to dynamo-electric maenergized under operating conditions at constant chines for generating direct-current electrical strength from that portion of the armature windenergy of the kind in which the armature current ing under the trailing pole portion of pole piece 5 under short-circuit conditions is limited to a I by being connected. across auxiliary brush 9 predetermined value and the open circuit voltage and main brush 5. The seri s field windings it is also limited to a predetermined value. Such and it are located on the leading portions of each generators are particularly applicable for supplyof the other pole pieces 2 and t and are connected ing energy for are welding and are sometimes in series with the main brushes 5'l and 6-8,

10 called constant current generators. which are interconnected as shown in the draw- 10 It is an object of my invention to povide a ing. The series field windings are connected so improved self-exciting direct-current generator as magnetically to oppose the shunt field windof the constant current type having an inherent ings. These series field windings each consist regulation suitable for maintaining a welding arc of a plurality of sections which are connected to or for supplying another load of similar chara tapping switch iii. For example, each series 15 acter. winding may comprise ce sections as illus- My invention will be best understood from a trated, and the tapping s .utch is arranged so as consideration of the embodiment illustrated in to have three operative positions, the series field the accompanying drawing which diagrammatlwindings being connected to the tapping switch cially illustrates a l-pole machine. so that a similar number of turns on each of the 20 According to my invention the main pole pieces leading pole portions are included in the armaare each radially slotted to form leading and ture circuit for any position of the tapping switch. trailing pole portions, and the trailing pole por- A rhcostat ii is provided in circuit with the tions are constructed and arranged to operate shunt field windings for controlling their effecsubstantially at magnetic saturation. Shunt field tiveness. Commutating pole pieces l8 located windings are provided around alternate pole between the main pole pieces and provided with pieces and series field windings are disposed on windings connected in the armature circuit may the leading portion of each of the other pole be provided as illustrated in the drawing.

pieces. The series field windings are connected The armature circuit of the machine proceeds go so as magnetically to oppose the shunt field windfrom brushes ii8 through the windings on the lugs, and the shunt field windings under opercommutating pole pieces l3 and thence by way ating conditions are energized at constant of the outer sections or the series field windings strength from that portion of the armature windit and iii to tap it which is connected by a ing under the trailing pole portion of one of the conductor 28 with a fixed contact 2! of switch pole pieces. The shunt field windings inherently iii. From tap it a circuit proceeds through the maintain the trailing pole portions of the pole middle sections of series field windings i5 and pieces substantially magnetically saturated irreit to a tap 22 whic is connected by a conductor spective of or assisted by the series field windings. 23 to a fixed contact 2 of switch l5. From tap The particular embodiment of my invention 22 a circuit proceeds by way of the inner sections illustrated in the drawing is provided with four of series field windings it and i5 and conductor 40 main pole pieces I, 2, 3, and l, four main brushes 25 to a fixed contact 26 of switch it. Switch it 5, 6, l, and 3, and an auxiliary brush s. Each is provided with a fixed contact which is of the pole pieces is provided with a slot ii] which connected to one side of the load circuit 28, 29, divides the pole piece into leading and trailing the other side of which is connected by a conpole portions, the direction of rotation being as d ctor to brushes of the machine. 45

indicated in the drawing. The main brushes and The movable contacts it of switch iii are electhe auxiliary brush en age a commutator ll trically connected with one another and mechaniwhich is connected to the armature winding (not cally supported on a drum which has operating shown) located between the pole pieces. The positions a, b, and c. In operating position a,

main brushes engage this commutator so that one-third of the series field windings i l, 65 are 50 their lines of commutation are between adjacent connected in circuit; in position b, two-thirds of pole pieces and the auxiliary brush this these se "ies field windings are connected circommutato-r so that its line of commutation is cuit; and in position 0, all of the series field under the slot in the main pole piece l. Shunt windings are connected in circuit.

field windings l2 and I3 are located on two The slots in the pole pieces are preferably 55 made relatively wide adjacent the air gap, in order to obtain good commutation at the auxiliary brush 9. The pole pieces are conveniently formed of laminated construction and the trailing pole portions, in order to provide the required magnetic saturation, may be notched or perforated over a. part of their length to constrict their cross-sectional area. The yoke of the field system may be of cast or laminated construction as desired.

Instead of employing tapped series windings the adjustment of the value of the short circuit current may be obtained by means of suitable diverting resistances or other means for controlling the eifectiveness of the series field windings.

Under operating conditions the shunt field windings are energized at constant strength and inherently maintain the trailing pole portions substantially magnetically saturated. The series field windings magnetically oppose the shunt field windings and assist in maintaining the magnetic saturation of the trailing portions of the pole pieces. As the armature current increases from zero, the reverse series field windings cause a reduction and eventually reverse the magnetic fluxes traversing the air gaps below the leading portions of the pole pieces and increased armature current thus causes a reduction of the resultant flux traversing the air gap, since the trailing pole portions are already saturated. Stability of operation is insured because the voltage across the shunt field windings is maintained substantially constant.

Limitation of short circuit current is obtained by the increase of the series field reversing flux with increased load current. The flux traversing the leading pole piece portions is thus progressively reduced as the armature current increases until the reverse flux from the series windings i4 and I5 counter-balances the excitation flux provided by the shunt field windings l2, l3. Thereafter, a further progressive increase of armature current produces a progressively increasing reversed flux in the leading pole piece portions which eventually will equal the flux traversing the trailing pole piece portions so that the resultant flux entering the armature is zero and no voltage is produced at the main brushes. The operation as above described depends, of course, upon the fact that the flux traversing the trailing pole piece portions is not increased correspondingly with the reduction, and eventual reversal, of the flux traversing the leading pole piece portions and this, of course, is due to the fact that the trailing pole piece portions are saturated under operating conditions. It is to be noted that if these trailing pole piece portions are not saturated at no load they are promptly saturated under load for they provide return paths for the flux set up in the leading pole piece portions: by the load current. Since under operating conditions the shunt windings l2, l3 are energized at a substantially constant voltage from conductors lying under the magnetically saturated trailing pole piece portions, stability of operation of the machine is insured.

Although I have particularly described my invention in connection with a 4-pole machine, it is obvious that my invention is not limited to such construction. Furthermore, various other modifications will be evident to those skilled in the art in view or" my disclosure and, accordingly, I seek to cover in the appended claims, all modifications which come within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A dynamo-electric machine having an armature winding and pole pieces each of which is radially slotted forming leading and trailing pole portions, the trailing pole portions being constructed and arranged to operate substantially at magnetic saturation, a shunt field winding on one of said pole pieces and a series field winding on the leading portion of an adjacent pole piece, said series field Winding being connected so as magnetically to oppose said shunt field winding, and said shunt field windin being energized under operating conditions at constant strength from, that portion of the armature winding under the trailing pole portion of one of said pole pieces.

2. A dynamo-electric machine having an armature winding and pole pieces each of which is radially slotted forming leading and trailing pole portions, the trailing pole portions being constructed and arranged to operate substantially at magnetic saturation, shunt field windings on alternate pole pieces, and series field windings on the leading portions of each of the other pole pieces, said series field windings being connected so as magnetically to oppose said shunt field windings and said shunt field windings being energized under operating conditions at constant strength from that portion of the armature winding under the trailing pole portion of one of said pole pieces.

3. A dynamo-electric machine having an armature winding and pole pieces each of which is radially slotted forming leading and trailing pole portions, said trailing pole portions being constructed and arranged to operate substantially at magnetic saturation, shunt field windings on alternate pole pieces energized under operating conditions at constant strength from that portion of the armature winding under the trailing pole portion of one of said pole pieces, series field windings on the leading portions of each of the other pole pieces connected so as magnetically to oppose said shunt field windings, and means for controlling the effectiveness of said series field windings.

4. A dynamo-electric machine having pole pieces each of which is radially slotted forming leading and trailing pole portions, the trailing pole portions being constructed and arranged to operate substantially at magnetic saturation, shunt field windings on alternate pole pieces, series field windings on the leading portions of each of the other pole pieces, an armature winding, 9. commutator connected to said armature winding, main brushes engaging said commutator so that their lines of commutation are between adjacent pole pieces, and an auxiliary brush engaging said commutator so that its line of commutation is under one of the slots provided in said pole pieces, said series windings being connected in circuit with said main brushes so as magnetically to oppose said shunt field windings, and said shunt field windings being connected between one of said main brushes and said auxiliary brush.

5. A dynamo-electric machine having pole pieces each of which is radially slotted forming leading and trailing pole portions, the trailing pole portions being constructed and arranged to operate substantially at magnetic saturation, shunt field windings on alternate pole pieces, series field windings on the leading portions of each of the other pole pieces, an armature winding, 9. commutator connected to said armature winding,

main brushes engaging said commutator so that their lines of commutation are between adjacent pole pieces, and an auxiliary brush engaging said commutator so that its line of commutation is under one of the slots provided in said pole pieces, said series field windings being connected in circuit with said main brushes so as magnetically to oppose said shunt field windings, said shunt field windings being connected between one of said main brushes and said auxiliary brush, and said slots being relatively wide adjacent the armature winding to obtain good commutation at said auxiliary brush.

6. A dynamo-electric machine having pole pieces each of which is radially slotted forming leading and trailing pole portions, the trailing pole portions being constructed and arranged to operate substantially at magnetic saturation, shunt field windings on alternate pole pieces,

20 means for controlling the effectiveness of said shunt field windings, series field windings on the leading portions of each of the other pole pieces, means for controlling the effectiveness of said series field windings, an armature winding, a commutator connected to said armature winding, main brushes engaging said commutator so that their lines of commutation are between adjacent pole pieces, and an auxiliary brush engaging said commutator so that its line of commutation is under one of the slots provided in said pole pieces, said series field windings being connected in circuit with said main brushes so as magnetically to oppose said shunt field windings, said shunt field windings being connected between one of said main brushes and said auxiliary brush, and said slots being relatively wide adjacent the armature winding to obtain good commutation at said auxiliary brush.

ALEXANDER GREENWOOD WILLIAMSON. 

